Make x86_64 log writer not use println!.
Make x86_64 log writer not use println!.

This opens the door to completely elimnating println! usage from the
kernel.

Signed-off-by: Wren Turkal <1c01a65c7a4125e8293dc90f61316d18ba72756a@penguintechs.org>

redox-os/kernel,redox-os/kernel,redox-os/kernel